Adjustable inductor



Nov. 2, 19485 E. OB RIE N 2,452,576 I ADJUSTABLE mnuc'ron Filed Aug 12, 1944 2 Sheets-Sheet 1 INV'ENTOR E a? 032mm,

. B Mf/Zm Nov. 2, 1948. E. OBRIEN ADJUSTABLE INDUCTOR 2 Sheets-Sheet 2 Filed. Aug. 12, 1944 f/yww INVI'ENTOR. 7" mism- Patented Nov. 2, 1948 hii'iE STATES "hi i 'ABJUSTAELE INDUCEOR Application August 12, 194%, Serial No. 543,2'25

2 Claims. 1

This invention relates to adjustabl inductors and, while it is of general application, itis particularly suitable for embodiment in an inductor used as acontinuously adjustable tuning element of a high-frequency tunable circuit, such as the tank circuit of a high-frequency oscillator.

Continuously adjustable inductors have Wide application as adjustable tuning elements in high.- frequency and u trah gh-frequency circuits. A great man continuously adjustable inductors have heretofore been proposed, one of the men forms comprising helical coil mounted on a rotatable insulation form and a sliding contact the conductor of the helical wind ing and movable lon itudii ally by such enrage- The circuit connec ons to the inductor Winding have generally been made by slip rings, while the connection to an intermediate point of the winding has been made through the sliding contact engaging the Winding and by the engagement of the contact with its c :iductive slice. Thus, there has been a total of four slidin or moving contacts found in the usual construc tion. Furthermore, in such prior art inductors, for convenience in adjustment and making cir" cuit connections. the structure has been open, with the result that the contacts have been eX- posed, thereby collecting dirt and d st usev As a result, such continuously adjustable inductors of the prior art have tended to be very noisy electrically in operation. Furthermore, when such an inductor is used as a coupling element, it is mechanicall and electrically difiicult to mount a secondary Winding with an accurately predetermined amount of coupl ng to the adjustable winding.

t s an object of the invention, therefore, to prev a new and improved adjustable inductor which overcomes one or more of the above-nan1ed disadvantages and limitations of the adjustable inductors of the prior art.

It is another object of the invention to provide a new and improved adjustable inductor which includes a In mum number of movable contacts and therefore is exceptionally quiet electrically in operation. It is another object of the invention to provide a new improved adjustable inductor in which the moving contacts are completely nclosed him the structure itself, thereby avoi -ng effects of accumulated dirt on the contacts.

It 'isanother object of the invention to provide a new and improved adjustable induct-or suitable for use as a coupling device by means of whicha secondary windin may be readily coupied thereto with an accurately predetermined mutual'inductance.

In accordance with the invention, an enclosed adjustable inductor comprises a tubular form of ternal contact element engaging the Wll'ldl -e inductor also includes means for mov g the contact element in a helical path While intaining a slilng engagement with the Winding and a pair of t ninals connected to electrically spaced points of the inductor.

In a preferred form of the invention, internal contact element and its me ns for me it. in a helical path comprise a conductive rod d sposed centrally in the form and havins a helical groove of the same pitch as the n g, a re tatable longitu nai g1 e m ans lu nalled on the rod, a contact member slidably s teal on the guide means and including a con lot eler agng the winding and a second co merit engaging the groove on the conch and electrically connected to the first conic ge her with means, such as a manua l oneknob, for rotating the guide means abot to cause the contact element to move in its h path.

For a better understanding of the invert-io elical together with other and further objects t f, reference is had to the follow dcs on in connection with the accompanyin ings While its scope will be pointed o appended claims.

Referr ng now to the drawin Fig. 1 is a longitudinal sectional view Pg. 2 is a cross ticnal view along the line 22 of Fig. l of cow tinuously adjustable inductor e odying i vention; Fig. 3 is a detail pel cect ve view or C Sac" movable contact structure embod d l..- the 4 is a sche- Lucite o latter two being transparent, thereby permitting inspection of the interior of the apparatus. The form it is provided with an internal helical groove l-fia on its inside wall in which is mounted a helical inductor H, which may be preformed and either threaded into the groove or contracted and sprung into the groove.

The inductor also includes an internal contact element engaging the inductor winding together with means for moving the contact element in a helical path while maintaining a sliding engagement with the winding. This internal contact element and its moving means are constructed in the form of a conductive rod l2 disposed centrally in form it and having formed thereon a helical groove 62a of the same pitch as the helical inductor winding ii. These means also include a rotatable longitudinal guide means disposed in the form it and preferably journalled on the rod E2, preferably consisting of a pair of parallel rods i3 and it secured at their ends to a pair of crosspieces l5 and i6 by screws, rivets, or the like. Secured to the crosspiece l5 by rivets, screws, or the like is a flanged shaft or hub IT, on the outer end of which is mounted means for rotating the guide means, such as a knob i8.

A contact member l9, Figs. 2 and 3, is slidably supported on the guide means; for example, it may comprise a disk-like element !9, provided with a pair of holes i9a sliding on the rods 13 and i i. The contact member [9 includes a contact element E90, including a grooved projection lfid adapted to engage the conductor of the helical winding ii. The contact member also includes a second contact element 596 provided with a pin-like proiection I91 engaging the groove 52a of the rod E2. The contact elements Etc and Edd are biased into engagement with the winding ii and the rod l2 by means of a double reversely bent leaf-spring 599. As indicated more clearly in Fig. 3, the member 59 is formed with a deep slot 5%, the inner end of which slides on rod i 2, while the spring'isg is in turn provided with edge slots ldh engaging the sides of the slot 5% so that the contact elements I90 and ifie are permitted limited radial movements within the slot 5% of the member 19 to maintain the desired contact pressures. The spring Hg is of conductive material, for example, spring brass or phosphor bronze, and electrically interconnects the contact elements 590 and 596 which may be secured thereto by riveting, welding, or the like.

The inductor structure also includes a pair of plates or insulation material secured to and closing the ends of the form l9 and supporting the contact member 59 and its associated contact elements and the contact-element moving means. Specifically, each of the end plates is preferably formed of a thermosetting plastic resin, such as Bakelite, one of the plates 25 being secured to one end of the form iii by means of screws Elia and supporting the grooved rod 12 as by engaging a shoulder lZb formed on the rod l2 which is locked to the plate it by means of a pair of loci: nuts We and washers 52d. The rod !2 is thus rigidly supported from the end plate 25 t i us from the form it only at one end. The other end plate H is similarly secured to form iii by screws Zia and includes a sleeve bearing or oushing Zib in which the operating hub or shaft '5 t The hub 17 includes a recess ila which is rotatably mounted or journalled on an end i2e of the rod i of reduced section. Thus, with the shaft l2 rigidly mounted in end plate 2%, the shaft ll journalled in end plate 2! and journalled on the end 52c of rod 52, and with the crosspiece l5 of the guide means slidably and rotatably mounted on the rod l2, the whole structure is secured together while permitting rotation of the guide means I3, I 5, l5, l5 and I1 within the form Ill and about the rod i2.

A secondary winding 22 of any desired number of turns is disposed about the form l0, its terminals being brought out to a pair of connection lugs 23 mounted on the end plate 25. The inductor may be provided with any number of electrically spaced terminals, such as a pair of terminals 2 5a and 24b, it being apparent that with the stationary form iii and winding H, the addition of intermediate terminals does not in any way complicate the construction or increase the number of movable contacts required. For example, the terminal 24a may be connected to a fixed point near one end of the winding H by means of a strap or loop connection 2&0 suitably soldered or otherwise bonded to the terminal 25a and to the winding H. The other terminal 241) is connected by means of a conductive strap 25 to the fixed conductive rod l2 and thus to the contact element ltd mounted in contact member l9 and engaging the winding II. The terminal 24?) may, if desired, also be connected to a fixed point near the other end of the winding H as by means of a loop or strap connection also soldered or otherwise bonded to the terminal 2% and the winding ll. With this connection, the portion of the inductor winding between the contact element 59d and the end to which the terminal 24%) is connected is effectively short-circuited. However, it will beunderstood that the electrical connections to any of the fixed points on the inductor winding H and to the adjustable contact element 9d may be made in accordance with the circuit requirements of the particular apparatus of which the inductor forms a part. A crossplate 26 of insulation material is secured to the end plates 29 and 2i by means of screws 25c and serves to increase the rigidity of the structure and to function as a terminal board or strip for the terminals 2 3a and 24-17.

The operation of the adjustable inductor will be apparent from the foregoing description. In brief, adjustment of the operating knob l8 is effective to rotate the guide mechanism I 3, i l, I5, 16 carrying the contact member [9. Due to the engagement of the pin IQ of the contact element [96 in the groove of the rod l2, which has the same pitch as the winding ll, rotation of the guide means causes rotation of the contact element lfid in engagement with the winding H and a simultaneous co-axial movement required to maintain the contact I901 in engagement with the winding 1 l. That is, the contact element id is positively driven axially so that it does not rely on its mere frictional engagement with the winding M. This feature enables the mechanism to operate reliably even under adverse climatic conditions, such as icing frequently encountered in aircraft apparatus at high altitudes. At the same time an electrical circuit is completed from the contact element lSd through the spring l9g, the contact element Hie, rod [2 and the conductive strap 25 to the terminal 2%. Thus, there appears between the terminals 24a and 2% a continuously adjustable portion of the inductor winding ll.

It will be noted that between the terminals 24a and 25b there are only two slidable or otherwise movable contacts; namely, the contact between the element lad and the winding II and the contact between the element 19:; and the rod I2. Furthermore, it will be seen that these contacts are inside of a completely enclosed, dustproof housing formed by the winding form In and the end plates alone and without the addition of any other housing means. As a result, the moving contacts are kept clean and free from dirt which would otherwise tend to impair the contacts and to make them electrically noisy. Also, it will be seen that a secondary winding 22 of any desired number of turns and configurations may be readily disposed on the outside of the form [0 so that its self-inductance and its mutual inductance with the winding 1 I can be readily predetermined and adjusted.

Referring now to Fig. 4, there is represented schematically an application of the adjustable inductor of the invention to the tunable antenna circuit of a wave-signal translating apparatus.

the inductor 30 is effective to tune the circuit 30,

constructed in accordance with the invention and provided with an adjustable contact 30a for short-circuiting a selected portion of the inductor winding. The inductor 39 is connected across a tuning condenser 3| which may be either fixed or adjustable, as indicated. The tuning circuit is connected between an antenna 32 and ground. The inductor 30 is provided with a secondary winding 39!) which is connected to a wave-signal translating apparatus which may be either a I receiver or transmitter, although the invention is particularly suitable for use in tunable circuits of a high-frequency radio transmitter. It will be apparent that adjustment of the contact 30a of the inductor 39 is effective to tune the circuit 39, 3| over a desired frequency range. At the same time, the proportioning and positioning of the secondary winding 3917 may be so selected that the coupling between the winding 30 and the winding 3% may be caused to vary in a preselected manner as the inductor 30 is adjusted over its operating range, thus to control the sensitivity and selectivity characteristics of the selector 30, 3|.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed as new is:

1. An adjustable inductor comprising a tubular form of insulation material, a helical inductor winding disposed on the inside wall of said form, a conductive rod disposed centrally in said form and having a helical groove of the same pitch as said winding, an internal contact member including a first contact element electrically engaging said winding and a second contact element engaging said groove, spring means biasing said first and second contact elements into engagement with said winding and groove respectively and electrically interconnecting said contact elements, means for rotating said member about said rod to cause said first contact element to move in a helical path while maintaining a sliding engagement with said winding, and a pair of terminals connected to electrically spaced points of said inductor, one of said terminals being connected to said rod, whereby the circuit between said terminals includes only two sliding contacts.

2. An adjustable inductor comprising, a tubular form of insulation material, a helical inductor winding disposed on the inside wall of said form, an internal contact element engaging said winding, means for moving said contact element in a helical path while maintaining a sliding engagement with said winding, an elongated fixed contact element, a second contact element having a continuous conductive connection with said first-named contact element and a sliding engagement with said fixed contact element, and a pair of terminals connected to electrically spaced points of said inductor, one of said terminals being connected to said fixed contact element, whereby the circuit between said terminals includes only two sliding contacts.

EDGAR OBRIEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,114,697 Hull Oct. 20, 1941 1,820,240 Michell Aug. 25, 1931 1,858,492 Gebhard et al May 17, 1932 1,860,722 Rudolph et al May 31, 1932 1,880,199 Gebhard et a1 Oct. 4, 1932 1,996,823 Osnos Apr. 9, 1935 

